For very simple products, “making a prototype” might simply mean pressing a button and sending a CAD file to a 3D printer. For the products we tend to work on, it means some initial analysis, the testing of a few hypotheses, some engineering design work, discussions with a few specialized suppliers about the feasibility of a certain approach (for production), purchasing parts and assembling them, having them tested based on a customized plan, and sending the prototype. Oh, and most products require several rounds of prototyping, especially if they include electronic parts.
All this takes a certain number of hours. It is better if we are straightforward and mention a minimum amount (which might end up being much higher for a given project), to avoid breeding unrealistic expectations.